Table 2. Comparison of Methicillin-resistant Staphylococcus aureus (MRSA) Acquisition Rates in the Intervention Intensive Care Unit (ICU) (2002-2007) and Control ICU (2005-2007).
| Intervention (Surgical) ICUa | Control (Medical) ICU | |||
|---|---|---|---|---|
| Crude Rates | Rate (per 1,000 pt-days at riskb) | Rate (per 1,000 pt-days at riskb) | ||
| Pre-intervention | 12.64 | 10.97 | ||
| Post-intervention | 10.03 | 11.33 | ||
| Percent change | −20.68% | +3.28% | ||
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| Time Series Modelc | Beta [95% CI] | p | Beta [95% CI] | p |
| Intervention | −2.62 [−5.19, −0.04] | 0.046 | −11.10 [−37.40, 15.19] | 0.395 |
| Adjusted MRSA colonization pressured |
30.79 [8.74, 52.85] | 0.007 | 22.90 [−13.36, 59.16] | 0.207 |
| AR(1) | -- | -- | 0.33 [−0.02, 0.67] | 0.061 |
| MA(4) | -- | -- | −0.89 [−1.00, −0.79] | 0.000 |
| Constant | 6.75 [2.14, 11.35] | 0.005 | 17.72 [−11.61, 47.04] | 0.227 |
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| Model parameters | ||||
| Adjusted R2 | 0.14 | 0.32 | ||
| Durbin-Watson statistic | 2.08 | 1.84 | ||
| Q(4) p-value | 0.71 | 0.65 | ||
| Q(8) p-value | 0.55 | 0.55 | ||
| Q(12) p-value | 0.62 | 0.73 | ||
Note: AR(1)= auto-regressive variable, 1; MA(4)= moving-average variable, 4. The inclusion of AR and MA terms in the model addressed serial correlation seen, as evidenced by the Durbin-Watson statistic and the Box-Ljung Q(k) tests of the unadjusted model.
Models are based on all available data for the surgical ICU (61months, 2002-2007) and medical ICU (24 months, 2005-2007).
See study methods for definition of patient-days at risk.
In the multivariate time series model, ‘beta’ indicates the magnitude and the direction of the variable in the model, while the p value and 95% CI indicate the precision and significance of the variable within the model.
Other factors considered for inclusion in the final model included: decubitus ulcers, tracheostomy, enteral feedings, central venous catheter utilization ratio, mechanical ventilator utilization ratio.